Lara Croft has become the latest victim of the financial crisis, with sales of her new game selling less well than expected, particularly in North America.

UK games developer Eidos warned that sales of Tomb Raider: Underworld had failed to meet expectations, wiping £20m off projected sales for this year. It said earnings would also be hit, which may force the company to renegotiate loan terms with its bank, Lloyds TSB. Last year the firm made a pre-tax loss of £136m.

Eidos admitted it sold only 1.5m copies of Underworld between 18 November, when the game was launched, and the end of 2008. The figure is below the firm's forecasts, mainly because of a slower start in North America. The launch of the game was also delayed by five months. "In a difficult North American economy we have seen retailers restricting inventory levels and triple-A products being discounted above our expectation," said Eidos.

Shares in Eidos crashed by 28% in early trading yesterday, dropping by 5p to 10p – another setback for Time Warner, which has replaced property entrepreneur Robert Tchenguiz as the biggest shareholder and recently raised its stake in the firm from 16% to nearly 20%. This prompted speculation that the US media firm could make a bid for the troubled computer games company, recently renamed from SCi Entertainment.

Computer games site GameSpot described it as a "competent but underwhelming platform game that has little to offer fans of the genre" and gave it a score of 5.5 out of 10. But other sites gave it positive reviews, and it made the top 10 chart in Europe for the six weeks from launch to Christmas.

Worried about further discounting, Eidos has revised its sales assumptions for Underworld and other video games, and now estimates annual revenues will range from £160m to £180m, below earlier forecasts of between £180m and £200m.

"Given revised profit expectations, we may need to enter into discussions with our lending bank regarding our June 2009 covenants," the firm said.

An Eidos spokesman said the company had "plenty of headroom" financially.

Eidos is optimistic about the forth­coming launch of its Batman: Arkham Asylum game, which is being promoted by Warner Bros and is being trailed on DVDs of the movie The Dark Knight.

Nick Batram at brokerage KBC Peel Hunt said yesterday's downgrade was obviously disappointing but not surprising given the state of the consumer market.

"Batman is a major second-half launch and given its importance to Time Warner we still expect this to happen," he said. But he warned that the Batman launch would have an impact on Eidos's finances only towards the end of its second half, so the group may have to speak to its lenders.